Rastering

There are several reasons to use rastering as part of your workflow:

1. You might not be able to see your crystal. This could be because of crystal size, feathery ice on the loop, etc.

2. If you do see it, your crystal might not be where you think it is. Both loop materials and reservoir solution will refract visible light.

3. Even if none of the above is the case, you still don’t know if every part of your crystal diffract as well.

All of which indicate that you should use the X-ray beam to locate and centre your samples.

Real vs. perceived crystal position.

Red is the true sample position, rendered without any refraction, while blue is where the sample would appear.

One shot (0D)

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Line (2D)

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Grid (3D)

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Free form

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[Still image of 0D]

[Still image of 1D]

[Still image of 2D]

[Gif of free form raster grid]

First of all, you probably know your samples better than anyone. Feel free to deviate from the outline below, as you see fit.

But, to the extent that a typical workflow exist, here’s what staff would recommend when care is needed:

1. Check your attenuation and detector distance. You probably want:

   1. High attenuation (>80% on MX2)

   2. Long sample to detector distance (>1 Å above your expected resolution. When in doubt, add 100 mm)

2. Take a One-shot raster

   1. The fastest way to put photons through your sample, and see if it diffracts. One or more 0D shots might be all you need to move on to the next sample.

3. Set up a Grid raster (2D)

   1. This will help you find the best location to centre the crosshairs on.

   2. Rotate the sample 90 degrees, before the next step.

4. Line (1D)

   1. You don’t need to do a full grid screen, as all you need now is to centre along this axis.

5. One-shot (0D)

   1. Optionally, confirm that your chosen location diffract as expected.

6. Collect screen

   1. This is a short dataset for quick assessment of what parameters to pick for the full dataset.

   2. Refer to the strategy section for tips on how.

7. Collect dataset

Figs

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3. sfasfa

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5. ads

6. feas

7. afe